The aim of this proposal is to obtain an understanding of two broad phenomena: 1) the role of phospholipids, especially the polar head groups, in membrane structure and function, and 2) the mechanisms that regulate phospholipid synthesis in relation to macromolecular synthesis and cell growth. Methods will be developed to manipulate the lipid composition of LM cells in tissue culture with respect to both the acyl group and the polar head group of the phospholipids. Subcellular membrane fractions, including the plasma membrane, endoplasmic reticulum and mitochondria, will be isolated from cells with different lipid compositions. The phospholipid and sterol content will be determined in order to make correlations with the physical and biochemical properties of the membranes. Physical properties of the membranes will be studied by electron spin resonance, circular dichroism and fluorescent techniques. A number of lipid-requiring enzymes will be studied to determine the effect of altering the lipid composition on their activity. This will include two enzyme systems that may require lateral mobility in the membrane for their function. These studies should give unique information on the contribution of phospholipids to the activity of membranous enzymes and the significance of "fluidity" for membrane structure and function. Another aspect of this work will utilize genetic and biochemical methods to study the relationship between the glycerol-3-phosphate acyltransferase and adenylate kinase. This study will test the hypothesis that when the rate of phospholipid synthesis is changed by chaning the activity of the acyltransferase, the activity of adenylate kinase is regulated. This in turn, regulates the rate of macromolecular synthesis and cell growth.